Browsing by Author "Liao, Vinson"
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Item Deducing subnanometer cluster size and shape distributions of heterogeneous supported catalysts(Nature Communications, 2023-04-08) Liao, Vinson; Cohen, Maximilian; Wang, Yifan; Vlachos, Dionisios G.Infrared (IR) spectra of adsorbate vibrational modes are sensitive to adsorbate/metal interactions, accurate, and easily obtainable in-situ or operando. While they are the gold standards for characterizing single-crystals and large nanoparticles, analogous spectra for highly dispersed heterogeneous catalysts consisting of single-atoms and ultra-small clusters are lacking. Here, we combine data-based approaches with physics-driven surrogate models to generate synthetic IR spectra from first-principles. We bypass the vast combinatorial space of clusters by determining viable, low-energy structures using machine-learned Hamiltonians, genetic algorithm optimization, and grand canonical Monte Carlo calculations. We obtain first-principles vibrations on this tractable ensemble and generate single-cluster primary spectra analogous to pure component gas-phase IR spectra. With such spectra as standards, we predict cluster size distributions from computational and experimental data, demonstrated in the case of CO adsorption on Pd/CeO2(111) catalysts, and quantify uncertainty using Bayesian Inference. We discuss extensions for characterizing complex materials towards closing the materials gap.Item Plasma-Enabled Ligand Removal for Improved Catalysis: Furfural Conversion on Pd/SiO2(ACS Nano, 2023-11-14) Nguyen, Darien K.; Vargheese,Vibin; Liao, Vinson; Dimitrakellis, Panagiotis; Sourav, Sagar; Zheng, Weiqing; Vlachos, Dionisios G.A nonthermal, atmospheric He/O2 plasma (NTAP) successfully removed polyvinylpyrrolidone (PVP) from Pd cubic nanoparticles supported on SiO2 quickly and controllably. Transmission electron microscopy (TEM) revealed that the shape and size of Pd nanoparticles remain intact during plasma treatment, unlike mild calcination, which causes sintering and polycrystallinity. Using Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS), we demonstrate the quantitative estimation of the PVP plasma removal rate and control of the nanoparticle synthesis. First-principles calculations of the XPS and CO FTIR spectra elucidate electron transfer from the ligand to the metal and allow for estimates of ligand coverages. Reactivity testing indicated that PVP surface crowding inhibits furfural conversion but does not alter furfural selectivity. Overall, the data demonstrate NTAP as a more efficient method than traditional calcination for organic ligand removal in nanoparticle synthesis.